1  /* Implement __enable_execute_stack using mprotect(2).
       2     Copyright (C) 2011-2023 Free Software Foundation, Inc.
       3  
       4     This file is part of GCC.
       5  
       6     GCC is free software; you can redistribute it and/or modify it under
       7     the terms of the GNU General Public License as published by the Free
       8     Software Foundation; either version 3, or (at your option) any later
       9     version.
      10  
      11     GCC is distributed in the hope that it will be useful, but WITHOUT ANY
      12     WARRANTY; without even the implied warranty of MERCHANTABILITY or
      13     FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
      14     for more details.
      15  
      16     Under Section 7 of GPL version 3, you are granted additional
      17     permissions described in the GCC Runtime Library Exception, version
      18     3.1, as published by the Free Software Foundation.
      19  
      20     You should have received a copy of the GNU General Public License and
      21     a copy of the GCC Runtime Library Exception along with this program;
      22     see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
      23     <http://www.gnu.org/licenses/>.  */
      24  
      25  #include <sys/mman.h>
      26  #include <unistd.h>
      27  #include <stdlib.h>
      28  
      29  #define STACK_PROT_RWX (PROT_READ | PROT_WRITE | PROT_EXEC)
      30  
      31  static int need_enable_exec_stack;
      32  
      33  static void check_enabling (void) __attribute__ ((unused));
      34  extern void __enable_execute_stack (void *);
      35  
      36  #if defined __sun__ && defined __svr4__
      37  static void __attribute__ ((constructor))
      38  check_enabling (void)
      39  {
      40    int prot = (int) sysconf (_SC_STACK_PROT);
      41  
      42    if (prot != STACK_PROT_RWX)
      43      need_enable_exec_stack = 1;
      44  }
      45  #else
      46  /* There is no way to query the execute permission of the stack, so
      47     we always issue the mprotect() call.  */
      48  
      49  static int need_enable_exec_stack = 1;
      50  #endif
      51  
      52  /* Attempt to turn on access permissions for the stack.  Unfortunately it
      53     is not possible to make this namespace-clean.*/
      54  
      55  void
      56  __enable_execute_stack (void *addr)
      57  {
      58    if (!need_enable_exec_stack)
      59      return;
      60    else
      61      {
      62        static long size, mask;
      63  
      64        if (size == 0) {
      65  	size = getpagesize ();
      66  	mask = ~(size - 1);
      67        }
      68  
      69        char *page = (char *) (((long) addr) & mask);
      70        char *end  = (char *)
      71  	((((long) (addr + __LIBGCC_TRAMPOLINE_SIZE__)) & mask) + size);
      72  
      73        if (mprotect (page, end - page, STACK_PROT_RWX) < 0)
      74  	/* Note that no errors should be emitted by this code; it is
      75  	   considered dangerous for library calls to send messages to
      76  	   stdout/stderr.  */
      77  	abort ();
      78      }
      79  }